Secondary battery

ABSTRACT

A secondary battery includes an electrode assembly, the electrode assembly having first and second electrode plates and a separator therebetween, a case accommodating the electrode assembly, and first and second electrode tabs respectively connected to the first and second electrode plates, the first electrode tab being formed of an aluminum alloy including 97 wt % to 98.5 wt % of aluminum (Al), 1 wt % to 3 wt % of iron (Fe), and 0 wt % to less than 1 wt % of an impurity.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2013-0143211, filed on Nov. 22, 2013,in the Korean Intellectual Property Office, and entitled: “SECONDARYBATTERY,” is incorporated by reference herein in its entirety.

BACKGROUND

1. Field

Embodiments relate to a secondary battery.

2. Description of the Related Art

Secondary batteries are chargeable and dischargeable. Low capacitybatteries that use single battery cells may be used as power sources forvarious small portable electronic devices such as cellular phones,camcorders, or the like. High power batteries, which may use, e.g., tensof battery cells connected to each other in a battery pack, may be usedas power sources for motor drive, such as in electric scooters, hybridelectric vehicles, or the like.

In general, an electronic device, such as a notebook computer, a mininotebook computer, a net book, a mobile computer, an ultra mobilepersonal computer (UMPC) or a portable multimedia player (PMP), uses abattery pack as a portable power source, and the battery pack may have aplurality of battery cells connected in series and/or in parallel. Thebattery pack may include a protective circuit module (PCM) forprotecting battery cells against over-charge, over-discharge, orover-current. The protective circuit module may be housed in a framewith the battery cells and may be welded to the electrode tabs.

Depending on the external shape, secondary batteries may be classifiedinto different types, for example, a cylindrical battery using acylindrical aluminum can, a prismatic battery using a prismatic aluminumcan, and a pouch type battery accommodated in a thin-plate pouch typecase. When they are used for motor drive of the machines requiring ahigh power source such as the hybrid electric vehicles, the secondarybatteries (or unit battery) may form a secondary battery module of highpower.

SUMMARY

Embodiments are directed to a secondary battery including an electrodeassembly, the electrode assembly having first and second electrodeplates and a separator therebetween, a case accommodating the electrodeassembly, and first and second electrode tabs connected to the first andsecond electrode plates, the first electrode tab being formed of analuminum alloy including 97 to 98.5 wt % of aluminum (Al), 1 to 3 wt %of iron (Fe), and 0 wt % to less than 1 wt % of an impurity.

The aluminum alloy may contain aluminum (Al) in an amount of 97 wt % to98 wt %.

The impurity may be one selected from silicon (Si) and copper (Cu).

The aluminum alloy may contain silicon (Si) in an amount of less than0.15 wt %.

The aluminum alloy may contain copper (Cu) in an amount of less than0.05 wt %.

The aluminum alloy may have a grain size in a range of 5 to 10 μm.

The aluminum alloy may have a tensile strength in a range of 80 to 110N/mm².

The aluminum alloy may have an elongation in a range of 17 to 38%.

The aluminum alloy may be bendable up to 13 to 30 times when it is bent180 degrees.

The aluminum alloy may have an electrical conductivity in a range of 50to 65% IACS, as defined by the international annealed copper standard(IACS).

The aluminum alloy may have resistance in a range of 68 to 85 Ω/Km.

The first electrode tab may extend outside the case.

The case may be a pouch, and the first electrode tab may be attached, ata location inside of the pouch, to the first electrode plate and mayextend through a sealing portion of the pouch to the outside of thepouch.

The first electrode tab may serve as a terminal at an outside of thecase.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates an exploded perspective view of a secondary batteryaccording to an example embodiment;

FIGS. 2 a and 2 b illustrate observation results of grain sizes ofaluminum alloys used in first electrode tabs of secondary batteriesaccording to Example 1 and Comparative Examples 1 and 2, as shown inTable 1; and

FIGS. 3 a and 3 b illustrate observation results of aluminum alloys usedin first electrode tabs of secondary batteries according to Example 1and Comparative Examples 1 and 2, as shown in Table 1.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art. In thedrawing figures, the dimensions of layers and regions may be exaggeratedfor clarity of illustration. Like reference numerals refer to likeelements throughout.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the embodiments. Asused herein, singular forms are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprise” and/or “comprising,” when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various members, elements, regions,layers, and/or parts, these members, elements, regions, layers, and/orparts should not be limited by these terms. These terms are merely usedto distinguish one member, element, region, layer, and/or part fromanother member, element, region, layer, and/or part. Thus, for example,a first member, element, region, layer, and/or part discussed belowcould be termed a second member, element, region, layer, and/or part.

Hereinafter, a configuration of a secondary battery according to anexample embodiment will be described.

FIG. 1 is an exploded perspective view of a secondary battery (100)according to an example embodiment.

Referring to FIG. 1, the secondary battery 100 according to an exampleembodiment may include an electrode assembly 110 and a case 120accommodating the electrode assembly 110.

In the present example embodiment, the electrode assembly 110 is formedby stacking or winding a first electrode plate 111, a second electrodeplate 112, and a separator 113 interposed between the first electrodeplate 111 and the second electrode plate 112. The first electrode plate111 may be a positive electrode and the second electrode plate 112 maybe a negative electrode, or vice versa.

When the first electrode plate 111 is a positive electrode plate, it maybe formed by coating a first active material layer on both surfaces of afirst current collector made of a metal thin plate having goodconductivity, such as an aluminum (Al) foil. A chalcogenide compound maybe used as the first active material, and examples thereof may include,e.g., composite metal oxides, such as LiCoO₂, LiMn₂O₄, LiNiO₂, orLiNiMnO₂.

According to the present example embodiment, the first electrode tab 114is formed on a first uncoated portion of the first electrode plate 111without a first active material layer formed thereon. For example, oneend of the first electrode tab 114 may be electrically connected to thefirst uncoated portion and the other end of the first electrode tab 114may be drawn to the outside of the case 120.

According to the present example embodiment, the first electrode tab 114may be formed of an aluminum alloy including 97 to 98.5 wt % of aluminum(Al), 1 to 3 wt % of iron (Fe), and 0 wt % to less than 1 wt % ofimpurity. The aluminum (Al) may be contained in an amount of 97 to 98 wt%. The impurity may include less than 0.15 wt % of silicon (Si) and lessthan 0.05 wt % of copper (Cu).

According to the present example embodiment, the first electrode tab 114may exhibit improved elongation and tensile strength, which may helpsecure stability during free fall of the secondary battery.

An insulating tape 116 for insulation may be attached to a regioncontacting the case 120 of the first electrode tab 114. The insulatingtape 116 may include, e.g., polyphenylene sulfide (PPS), polyimide (PI),polypropylene (PP), etc.

When the second electrode plate 112 is a negative electrode, it may beformed by coating a second active material layer on both surfaces of asecond current collector made of a conductive metal thin plate, such asa copper (Cu) or nickel (Ni) foil. A carbon-based material, Si, Sn, tinoxide, a tin alloy compound, a transition metal oxide, lithium metalnitride, metal oxide, etc., may be used as the second active material.

According to the present example embodiment, the second electrode tab115 is formed on a second uncoated portion of the second electrode plate112 without a second active material layer formed thereon. For example,one end of the second electrode tab 115 may be electrically connected tothe first uncoated portion and the other end of the second electrode tab115 may be drawn to the outside of the case 120.

According to the present example embodiment, the second electrode tab115 may be formed of a nickel (Ni) alloy. The insulating tape 116 forinsulation maybe attached to a region contacting the case 120 of thesecond electrode tab 115.

According to the present example embodiment, the separator 113 isinterposed between the first electrode plate 111 and the secondelectrode plate 112 in order to prevent a short-circuit between thefirst and second electrode plates 111 and 112. The separator 113 mayinclude, e.g., one or more of polyethylene, polypropylene, or acopolymer of polyethylene and polypropylene. The separator 113 may havea width larger than that of the first or second electrode plate 111, 112to prevent the short-circuit between the first and second electrodeplates 111 and 112.

According to the present example embodiment, the case 120 includes anupper case 121 and a lower case 122 produced by bending a mid portion ofone side of an integrally formed rectangular pouch film in a lengthwisedirection. A groove 123 in which the electrode assembly 110 is to bereceived is formed in the lower case 122 by pressing, and a sealing part122 a to be sealed with the upper case 121 is formed in the lower case122.

According to an example embodiment, the secondary battery 100 employs analuminum alloy including 97 to 98.5 wt % of aluminum (Al), 1 to 3 wt %of iron (Fe), and less than 1 wt % of impurity as a material of theelectrode tab 114. The electrode tab 114 of the secondary battery 100may have improved tensile strength and elongation, which may help securestability and reliability of the secondary battery during free fall.

Physical properties of the aluminum alloy used in the first electrodetab 114 were tested. Table 1 shows compositions of aluminum alloys usedin the first electrode tabs according to Example 1 and ComparativeExamples 1 and 2 (units: wt %)

TABLE 1 Si Fe Cu Mn Mg Zn Al Example 1 ≦0.15 1-3 ≦0.05 — — — 97-98.5Comparative ≦0.7 ≦0.1 ≦0.05 ≦0.05 ≦0.1 ≧99.3 Example 1 Comparative ≦0.7≦0.05 ≦0.05 ≦0.05 ≦0.1 ≧99.3 Example 2

Grain sizes, tensile strengths, elongation rates, and falling testresults will now be described with reference to Example 1 andComparative Examples 1 and 2, as shown in Table 1.

Grain Sizes and Surface States after Bending

FIGS. 2 a and 2 b illustrate observation results of grain sizes ofaluminum alloys used in first electrode tabs of secondary batteriesaccording to Example 1 and Comparative Examples 1 and 2, as shown inTable 1, and FIGS. 3 a and 3 b illustrate observation results ofaluminum alloys used in first electrode tabs of secondary batteriesaccording to Example 1 and Comparative Examples 1 and 2, as shown inTable 1.

FIGS. 2 a and 3 a show observation results of grain sizes and surfacestates in Example 1, and FIGS. 2 b and 3 b show observation results ofgrain sizes and surface states in Comparative Example 1. The grain sizesand surface states in Example 1 and Comparative Example 1 were observedby high-resolution scanning electron microscopy (SEM).

Referring to FIGS. 2 a and 2 b, the grain sizes in Example 1 weresmaller than those in Comparative Example 1. The grain sizes in Example1 were in the range of 5 to 10 μm, and the grain sizes in ComparativeExample 1 were in the range of 30 to 90 μm. Without being bound bytheory, it is believed that the aluminum alloy having relatively smallgrain sizes was superior in bendability, and demonstrated high stabilityagainst free fall or external impacts.

Referring to FIGS. 3 a and 3 b, in terms of surface states afterbending, the aluminum alloy of Example 1 had a smoother surface than thealuminum alloy of Comparative Example 1. Without being bound by theory,it believed that cracks were generated on the aluminum alloy ofComparative Example 1.

Tensile Strength and Elongation

Table 2 shows measuring results of tensile strengths and elongationrates in Example 1 and Comparative Example 1, as shown in Table 1. Here,test pieces used in Example 1 and Comparative Example 1 had a length of200 mm. For each, 25 test pieces having composition ratios of Example 1and Comparative Example 1 were used. The tensile strength was measuredusing a tensile strength measuring device (Model name: RTC-1210manufactured by Orientec, Co., Ltd.), Here, the tension speed was 50mm/min and gauge length of test pieces were 100 mm. Assuming that thegauge length was 100 mm is denoted by reference symbol A and a rupturedgauge length when the test piece was extended is denoted by referencesymbol A′, the elongation can be defined in Equation (1):

Elongation (%)={(A′−A)/A}×100  (1)

TABLE 2 Tensile strength (N/mm²) Elongation (%) Com- Com- par- par-ative ative Exam- Exam- Exam- Exam- N = 25 ple 1 ple 1 ple 1 ple 1 174.1 94.9 17.8 26.2 2 74.8 96.6 20.4 24.8 3 73.5 95.7 17.8 26.4 4 74.497.7 16.5 26.8 5 74.8 94.9 17 20.2 6 72.6 96.2 14.5 24.8 7 72.4 97.715.5 25 8 74.6 96.3 16.6 23.6 9 74.4 97.3 19.1 24 10 73.1 95.2 18.9 28.311 74 95.6 18.7 25 12 73.4 94.9 19.8 23.6 13 73.4 94.9 19.4 26.3 14 73.894.7 18.7 25.2 15 73.7 96.9 17.2 19.9 16 73.9 94.3 17.9 26.8 17 73.794.8 18.3 26.3 18 74.4 95.2 18.5 25.5 19 73.3 98.4 14.6 24.5 20 72.794.4 16.5 22.2 21 73.2 95 16.8 23.2 22 73.1 95.4 18.4 24 23 72.5 95 1524.8 24 74.5 94.7 19.4 24.5 25 73 95.2 17.7 25.3 Maximum 74.8 98.4 20.428.3 value Minimum 72.4 94.3 14.5 19.9 value Mean 73.625 95.676 17.6424.688

Referring to Table 2, the electrode tabs of Example 1 demonstrated95.676 N/mm² in mean value of tensile strength, which was superior tothe mean value of tensile strength of the electrode tabs of ComparativeExample 1, that is, 73.625 N/mm². In addition, the electrode tabs ofExample 1 demonstrated 24.688% in mean value of elongation, which wassuperior to the mean value of elongation of the electrode tabs ofComparative Example 1, that is, 17.64%. Accordingly, the electrode tabsaccording to Example 1 may provide excellent tensile strength andelongation, which may help secure stability and reliability of thesecondary battery, and may not easily be ruptured free fall or externalimpacts.

Free Fall Test

Tables 3a and 3b show free fall test results of secondary batteriesemploying first electrode tabs having composition ratios of Example 1and Comparative Examples 1 and 2.

Soft tabs 1, 2, 3, 4, and 5 had a composition ratio of Example 1 shownin Table 1, and hard tabs 1, 2, 3, 4, and 5 had a composition ratio ofone of Comparative Examples 1 and 2 shown in Table 1.

The free fall tests were carried out after exposing the secondarybatteries employing the respective electrode tabs underhigh-temperature, high-humidity conditions of 60° C., and 90% RH for 72hours. Tables 3a and 3b show initial open circuit voltages (OCVs)measured after exposing the secondary batteries under high-temperature,high-humidity conditions for 72 hours, and OCVs measured by allowing thesecondary batteries to fall step by step and measuring whenever thefalling was completed. The falling steps were carried out a total of7000 counts of falling steps as follows: (1) 1250 counts on frontsurfaces; (2) 1250 counts on rear surfaces; (3) 750 counts on leftsides; (4) 750 counts on right sides; (5) 250 counts on bottom sides;(6) 500 counts on bottom sides; (7) 750 counts on bottom sides; (8) 250counts on top sides; (9) 500 counts on top sides; and (10) 750 counts ontop sides. It was determined whether a secondary battery was defectiveor not by checking whether it had a normal voltage by comparing theinitial OCV and an OCV measured after each falling step. Thus, theinitial OCV was compared with the OCV for each falling step carried outon each secondary battery, and if the secondary battery had a constantvoltage, it was determined that the secondary battery was normal.However, if there was a change in the voltage of the secondary battery,the first electrode tab of the secondary battery was expected to be cut,and it was determined that the secondary battery was defective.

TABLE 3a Steps Initial (Accumulated OCV (1) (2) (3) (4) (5) counts) (0)(1250) (2500) (3250) (4000) (4250) Soft tab 1 3.8392 3.8393 3.83933.8391 3.8392 3.8392 Soft tab 2 3.8396 3.8397 3.8397 3.8396 3.83963.8396 Soft tab 3 3.8395 3.8396 3.8395 3.8395 3.8395 3.8394 Soft tab 43.8402 3.8403 3.8403 3.8402 3.8402 3.8402 Soft tab 5 3.8389 3.83913.8391 3.839 3.839 3.8399 Hard tab 1 3.8409 3.8409 3.8409 3.8409 3.84083.8408 Hard tab 2 3.8431 3.8431 3.8431 3.8431 3.8431 3.8431 Hard tab 33.8439 3.8438 3.8438 3.8438 3.8438 3.8438 Hard tab 4 3.8454 3.84543.8454 3.8453 3.8453 3.8453 Hard tab 5 3.8424 3.8423 3.8423 3.84233.8422 3.8422

TABLE 3b Steps (Accumulated (6) (7) (8) (9) (10) counts) (4750) (5500)(5750) (6250) (7000) Results Soft tab 1 3.8391 3.8391 3.8391 3.83913.8391 OK Soft tab 2 3.8395 3.8395 3.8395 3.8395 3.8395 OK Soft tab 33.8394 3.8394 3.8394 3.8394 0.7377 NG (NG) Soft tab 4 3.8401 3.84013.8402 3.8402 3.8402 OK Soft tab 5 3.8389 3.8389 3.8389 3.8389 3.8389 OKHard tab 1 3.8408 0.8556 — — — NG (NG) Hard tab 2 3.843 0.9182 — — — NG(NG) Hard tab 3 3.8438 3.8438 3.8437 3.8437 3.8438 OK Hard tab 4 3.84530.7505 — — — NG (NG) Hard tab 5 0.732 — — — — NG (NG)

Referring to Tables 3a and 3b, secondary batteries employing soft tabs1, 2, 3, 4, and 5 demonstrated relatively constant voltages up to 5500counts of falling steps, suggesting that they were in relatively goodstates, while secondary batteries employing hard tabs 1, 2, 4, and 5demonstrated sharp voltage drops after 5500 counts of falling steps,suggesting that they were defective. In particular, it was confirmedthat defects occurred to the secondary battery employing the hard tab 5after 4750 counts of falling steps, suggesting that the secondarybattery employing the hard tabs was brittle against the free fall. Inaddition, for up to 7000 counts of falling steps, most secondarybatteries having composition ratios of Example 1 (except for thesecondary battery employing the soft tab 3 determined as beingdefective) had superior properties. In contrast, the secondary batteriesemploying hard tabs 1, 2, 4, and 5 were determined to be defective.

Physical Properties of Note

Table 4 shows physical properties of note for aluminum alloys accordingto Example 1 and Comparative Example 1 shown in Table 1. Here, thebendability is indicated by the maximum number of bending counts withoutbeing ruptured when the electrode tabs according to Example 1 andComparative Example 1 were bent 180 degrees. In addition, the electricalconductivity is defined in percentile by the International AnnealedCopper Standard (IACS), assuming that the conductivity of pure copper(1.73×10⁻⁸ Ωm) is set to 100% IACS.

TABLE 4 Tensile Electrical Resis- strength Elongation Bendabilityconductivity tance (N/mm²) (%) (Times) (% IACS) (Ω/Km) Example 1 90-10020-28 16-20 55-60 73-77 Comparative 70-80  15-23 10-14 59-61 75-78Example 1

Referring to Table 4, the electrode tabs of Example 1 demonstrated 50 to65% IACS, more particularly 55 to 60% IACS, in electrical conductivity,which was a similar level to the electrical conductivity of theelectrode tabs of Comparative Example 1, that is, 59 to 61% IACS. Inaddition, the electrode tabs of Example 1 demonstrated 68 to 85 Ω/Km,more particularly 73 to 77 Ω/Km, in resistance, which was a similarlevel as the resistance of the electrode tabs of Comparative Example 1,that is, 75 to 78 Ω/Km. In view of elongation, the electrode tabs ofExample 1 demonstrated 80 to 110 N/mm² in tensile strength and 17 to 38%in elongation, more particularly 90 to 100 N/mm² in tensile strength and20 to 28% in elongation, which were superior to the tensile strength andelongation of the electrode tabs of Comparative Example 1, that is, 70to 80 N/mm² and 15 to 23%, respectively. In addition, in Example 1, theelectrode tabs were bendable 13 to 30 times, more particularly 16 to 20times, when they were bent 180 degrees, suggesting that the electrodetabs of Example 1 were superior to the electrode tabs of ComparativeExample 1, which were bendable 10 to 14 times, in view of bendability.The electrode tabs of Example 1 were made of soft materials, compared tothe electrode tabs of Comparative Example 1, and demonstratedflexibility without being cut during free fall tests of the secondarybatteries, which may help secure the stability and reliability ofsecondary battery.

By way of summation and review, a secondary battery may be constructedby accommodating an electrode assembly (which may be formed by insertinga separator as an insulator between positive and negative electrodeplates) in a case together with an electrolytic solution. Electrode tabsmay be used as terminal portions of positive and negative electrodes,and may be connected to the positive and negative electrode plates tothen be drawn to the outside of the case. During a falling test (fordetermining reliability of the secondary battery), the electrode tabs,e.g., the positive electrode tab, may be cut at a boundary regionbetween the case and the positive electrode tab, which may make itdifficult to use electrode tabs as terminal portions.

As described above, embodiments may provide a secondary battery, whichmay include an electrode tab formed of a material that improves tensilestrength and elongation. The secondary battery may be stable whensubjected to a free fall.

As described above, the secondary battery according to embodiments mayimprove a tensile strength and an elongation rate by forming a positiveelectrode tab using an aluminum alloy including 97 to 98.5 wt % ofaluminum (Al), 1 to 3 wt % of iron (Fe) and less than 1 wt % ofimpurity, which may help secure stability during free fall.

As described above, the secondary battery 100 according to an exampleembodiment employs an aluminum alloy including 97 to 98.5 wt % ofaluminum (Al), 1 to 3 wt % of iron (Fe) and less than 1 wt % of impurityas the first electrode tab 114. In a secondary battery using anelectrode tab having excellent tensile strength, elongation andbendability, it may be possible to prevent the electrode tab from beingcut during free fall, which may help secure stability and reliability ofthe secondary battery.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A secondary battery, comprising: an electrodeassembly, the electrode assembly having first and second electrodeplates and a separator therebetween; a case accommodating the electrodeassembly; and first and second electrode tabs respectively connected tothe first and second electrode plates, the first electrode tab beingformed of an aluminum alloy including 97 wt % to 98.5 wt % of aluminum(Al), 1 wt % to 3 wt % of iron (Fe), and 0 wt % to less than 1 wt % ofan impurity.
 2. The secondary battery as claimed in claim 1, wherein thealuminum alloy contains aluminum (Al) in an amount of 97 wt % to 98 wt%.
 3. The secondary battery as claimed in claim 1, wherein the impurityis one selected from silicon (Si) and copper (Cu).
 4. The secondarybattery as claimed in claim 3, wherein aluminum alloy contains silicon(Si) in an amount of 0 wt % to less than 0.15 wt %.
 5. The secondarybattery as claimed in claim 3, wherein aluminum alloy contains copper(Cu) in an amount of 0 wt % to less than 0.05 wt %.
 6. The secondarybattery as claimed in claim 1, wherein the aluminum alloy has a grainsize in a range of 5 to 10 μm.
 7. The secondary battery as claimed inclaim 1, wherein the aluminum alloy has a tensile strength in a range of80 to 110 N/mm².
 8. The secondary battery as claimed in claim 1, whereinthe aluminum alloy has elongation in a range of 17 to 38%.
 9. Thesecondary battery as claimed in claim 1, wherein the aluminum alloy isbendable up to 13 to 30 times when it is bent 180 degrees.
 10. Thesecondary battery as claimed in claim 1, wherein the aluminum alloy haselectrical conductivity in a range of 50 to 65% IACS, as defined by theinternational annealed copper standard (IACS).
 11. The secondary batteryas claimed in claim 1, wherein the aluminum alloy has resistance in arange of 68 to 85 Ω/Km.
 12. The secondary battery as claimed in claim 1,wherein the first electrode tab extends outside the case.
 13. Thesecondary battery as claimed in claim 12, wherein the case is a pouch,and the first electrode tab is attached, at a location inside of thepouch, to the first electrode plate and extends through a sealingportion of the pouch to the outside of the pouch.
 14. The secondarybattery as claimed in claim 12, wherein the first electrode tab servesas a terminal at an outside of the case.